1. Field of the Invention
This invention relates to a design for an electrode assembly for a plural cell electrolyzer and more particularly to a design which provides a cathode with an essentially flat surface for use in the electrolysis of brine for production of chlorine and caustic soda.
2. Description of the Prior Art
The electrolysis of sodium chloride brine is by far the most important commercial process for producing chlorine and caustic soda. Recently, there has been tremendous commercial interest in electrolysis cells incorporating metallic anodes rather than graphite anodes used theretofore in this process. Further, there is evolving a clear trend toward the use of cationic permselective membranes rather than conventional permeable deposited asbestos diaphragms in these cells. The permselective membranes differ substantially from the permeable diaphragms in that no hydraulic flow from anode to cathode compartments is permitted. The permselective membranes, typically ion exchange resins cast in the form of very thin sheet, consist of a perfluorinated organic polymer matrix to which ionogenic sulfonate groups are attached. Thus, during electrolysis of sodium chloride brine the negatively charged groups permit transference of current-carrying sodium ions across the membrane while excluding chloride ions. Consequently, it is not possible to produce caustic soda of a predetermined concentration and nearly free of chloride within the cathode compartment.
Maximum utility of a system incorporating metallic anodes and permselective membranes is achieved by a multicell design wherein cells are arranged in serial fashion. An anode mounted on one cell frame faces the cathode mounted on the adjoining cell frame. Between the two cell frames is interposed a cationic permselective membrane. In a configuration such as this, it is important to have the paired anode and cathode parallel to each other. This permits one to minimize the interelectrode gap and the cell voltage drop due to the fluid paths in the cathode and anode chambers.
U.S. Pat. No. 4,115,236 discloses an intercell connector which provides direct electrical communication and secure mechanical connection between cells of an electrolyzer. Although that device provides a significant advance over the prior art, it involves joining adjacent electrodes with four connectors, each mating with a separate cathode boss. Using that design, it may be difficult to produce a cathode with a flat surface, since this in effect requires that the four boss surfaces be coplanar. Also, unless the cathode boss surfaces are coplanar, when the interelectrode connections are made, distorting forces are transmitted to the cell frame and/or to the anode bosses. These forces can cause loss of flatness in the anode.